If the flight is a 762, then she will likely end up w/a seat in the J, not F, cabin. IME when this happens, those who purchased J cabin seats are moved forward, rather than those flying on award or upgrade tickets.

Of course, that doesn't mean that when this happened to another poster's sister's dentist's cousin . . . , that said cousin ended up in F. It could happen, yes, but IME, Z on a two class becomes U on a three class.

Also, I would call the EXP line and get Mom's seat taken care of now rather than having her deal w/it at ORD.